Mesenchymal stem cells (MSCs) are the formative pluripotent blast or embryonic-like cells found in bone marrow, blood, dermis, and periosteum that are capable of differentiating into specific types of mesenchymal or connective tissues including adipose, osseous, cartilaginous, elastic, muscular, and fibrous connective tissues. The specific differentiation pathway which these cells enter depends upon various influences from mechanical influences and/or endogenous bioactive factors, such as growth factors, cytokines, and/or local microenvironmental conditions established by host tissues.
In prenatal organisms, the differentiation of MSCs into specialized connective tissue cells is well established; for example embryonic chick, mouse or human limb bud mesenchymal cells differentiate into cartilage, bone and other connective tissues (Caplan A I (1981) In: 39th Annual Symposium of the Society for Developmental Biology, ed by S. Subtelney and U Abbott, pp 3768. New York, Alan R Liss Inc; Elmer et al. (1981) Teratology, 24:215–223; Hauschka S. D. (1974) Developmental Biology (1974) 37:345–368; Solursh et al. (1981) Developmental Biology, 83:9–19; Swalla et. al. (1986) Developmental Biology, 116:31–38. In addition, a clonal rat fetus calvarial cell line has also been shown to differentiate into muscle, fat, cartilage, and bone (Goshima et al. (1991) Clin Orthop Rel Res. 269:274–283. The existence of MSCs in post-natal organisms has not been widely studied with the objective of showing the differentiation of post-embryonic cells into several mesodermal phenotypes. The few studies which have been done involve the formation of bone and cartilage by bone marrow cells following their encasement in diffusion chambers and in vivo transplantation (Ashton et al. (1980) Clin Orthop Rel Res, 151:294–307; Bruder et al. (1990) Bone Mineral, 11:141–151, 1990). Recently, cells from chick periosteum have been isolated, expanded in culture, and, under high density conditions in vitro, shown to differentiate into cartilage and bone (Nakahara et al. (1991) Exp Cell Res, 195:492–503). Rat bone marrow-derived mesenchymal cells have been shown to have the capacity to differentiate into osteoblasts and chondrocytes when implanted in vivo (Dennis et al. (1991) Cell Transpl, 1:2332; Goshima et al. (1991) Clin Orthop Rel Res. 269:274–283). Work by Johnstone et al. U.S. Pat. No. 5,908,784 has shown the ability of mesenchymal cells derived from skin to differentiate into cells biochemically and phenotypically similar to chondrocytes.
The adult bone marrow microenvironment is a potential source for these hypothetical mesodermal stem cells. Cells isolated from adult marrow are referred to by a variety of names, including stromal cells, stromal stem cells, mesenchymal stem cells (MSCs), mesenchymal fibroblasts, reticular-endothelial cells, and Westen-Bainton cells (Gimble et al. (November 1996) Bone 19(5): 421–8). In vitro studies have determined that these cells can differentiate along multiple mesodermal or mesenchymal lineage pathways. These include, but are not limited to, adipocytes (Gimble, et al. (1992) J. Cell Biochem. 50:73–82, chondrocytes; Caplan, et al. (1998) J Bone Joint Surg. Am. 80(12):1745–57; hematopoietic supporting cells, Gimble, et al. (1992) J. Cell Biochem. 50:73–82; myocytes, Prockop, et al. (1999) J. Cell Biochem. 72(4):570–85; myocytes, Charbord, et al. (1999) Exp. Hematol. 27(12):1782–95; and osteoblasts, Beresford et al. (1993) J. Cell Physiol. 154:317–328). The bone marrow has been proposed as a source of stromal stem cells for the regeneration of bone, cartilage, muscle, adipose tissue, and other mesenchymal derived organs. The major limitations to the use of these cells are the difficulty and risk attendant upon bone marrow biopsy procedures and the low yield of stem cells from this source.
Adipose tissue offers a potential alternative to the bone marrow as a source of multipotential stromal stem cells. Adipose tissue is readily accessible and abundant in many individuals. Obesity is a condition of epidemic proportions in the United States, where over 50% of adults exceed the recommended BMI based on their height. Adipocytes can be harvested by liposuction on an outpatient basis. This is a relatively non-invasive procedure with cosmetic effects that are acceptable to the vast majority of patients. It is well documented that adipocytes are a replenishable cell population. Even after surgical removal by liposuction or other procedures, it is common to see a recurrence of adipocytes in an individual over time. This suggests that adipose tissue contains stromal stem cells which are capable of self-renewal.
Pathologic evidence suggests that adipose-derived stromal cells are capable of differentiation along multiple mesenchymal lineages. The most common soft tissue tumor, liposarcomas, develop from adipocyte-like cells. Soft tissue tumors of mixed origin are relatively common. These may include elements of adipose tissue, muscle (smooth or skeletal), cartilage, and/or bone. Just as bone forming cells within the bone marrow can differentiate into adipocytes or fat cells, the extramedullary adipocytes are capable of forming osteoblasts (Halvorsen WO 99/28444).
Cartilage is a hyperhydrated structure with water comprising 70% to 80% of its weight. The remaining 20% to 30% comprises type II collagen and proteoglycan. The collagen usually accounts for 70% of the dry weight of cartilage (in “Pathology” (1988) Eds. Rubin & Farber, J. B. Lippincott Company, PA. pp. 1369–1371). Proteoglycans are composed of a central protein core from which long chains of polysaccharides extend. These polysaccharides, called glycosaminoglycans, include: chondroitin-4-sulfate, chondroitin-6-sulfate, and keratan sulfate. Cartilage has a characteristic structural organization consisting of chondrogenic cells dispersed within an endogenously produced and secreted extracellular matrix. The cavities in the matrix which contain the chondrocytes are called cartilage lacunae. Unlike bone, cartilage is neither innervated nor penetrated by either the vascular or lymphatic systems (Clemente (1984) in “Gray's Anatomy, 30.sup.th Edit,” Lea & Febiger).
Three types of cartilage are present in mammals and include: hyaline cartilage; fibrocartilage and elastic cartilage (Rubin and Farber, supra). Hyaline cartilage consists of a gristly mass having a firm, elastic consistency, is translucent and is pearly blue in color. Hyaline cartilage is predominantly found on the articulating surfaces of articulating joints. It is found also in epiphyseal plates, costal cartilage, tracheal cartilage, bronchial cartilage and nasal cartilage. Fibrocartilage is essentially the same as hyaline cartilage except that it contains fibrils of type I collagen that add tensile strength to the cartilage. The collagenous fibers are arranged in bundles, with the cartilage cells located between the bundles. Fibrocartilage is found commonly in the annulus fibrosis of the invertebral disc, tendinous and ligamentous insertions, menisci, the symphysis pubis, and insertions of joint capsules. Elastic cartilage also is similar to hyaline cartilage except that it contains fibers of elastin. It is more opaque than hyaline cartilage and is more flexible and pliant. These characteristics are defined in part by the elastic fibers embedded in the cartilage matrix. Typically, elastic cartilage is present in the pinna of the ears, the epiglottis, and the larynx.
The surfaces of articulating bones in mammalian joints are covered with articular cartilage. The articular cartilage prevents direct contact of the opposing bone surfaces and permits the near frictionless movement of the articulating bones relative to one another (Clemente, supra). Two types of articular cartilage defects are commonly observed in mammals and include full-thickness and partial-thickness defects. The two-types of defects differ not only in the extent of physical damage but also in the nature of repair response each type of lesion elicits.
Full-thickness articular cartilage defects include damage to the articular cartilage, the underlying subchondral bone tissue, and the calcified layer of cartilage located between the articular cartilage and the subchondral bone. Full-thickness defects typically arise during severe trauma of the joint or during the late stages of degenerative joint diseases, for example, during osteoarthritis. Since the subchondral bone tissue is both innervated and vascularized, damage to this tissue is often painful. The repair reaction induced by damage to the subchondral bone usually results in the formation of fibrocartilage at the site of the full-thickness defect. Fibrocartilage, however, lacks the biomechanical properties of articular cartilage and fails to persist in the joint on a long term basis.
Partial-thickness articular cartilage defects are restricted to the cartilage tissue itself. These defects usually include fissures or clefts in the articulating surface of the cartilage. Partial-thickness defects are caused by mechanical arrangements of the joint which in turn induce wearing of the cartilage tissue within the joint. In the absence of innervation and vasculature, partial-thickness defects do not elicit repair responses and therefore tend not to heal. Although painless, partial-thickness defects often degenerate into full-thickness defects.
In accordance with the present invention it has been observed by the inventors that when human adipose tissue-derived stromal cells are associated in a three-dimensional format they can be induced to commit and differentiate along the chondrogenic pathway when contacted in vitro with certain chondroinductive agents or factors. The three dimensional format is critical to the in vitro chondrogenesis of the invention and the cells are—preferably condensed together, for example, as a packed or pelleted cell mass or in an alginate matrix. This invention presents examples of methods and composition for the isolation, differentiation, and characterization of adult human extramedullary adipose tissue stromal cells along the chondrocyte lineage and outlines their use for the treatment of a number of human conditions and diseases. This in vitro process is believed to recapitulate that which occurs in vivo and can be used to facilitate repair of cartilage in vivo in mammals.